Conventional turbine airfoils used in blades and vanes of gas turbine engines have a trailing edge that is thin for aerodynamic efficiency. However, a lack of cooling surface area on the interior makes it difficult to cool the thin trailing edge. The trailing edge is typically cast integrally with the entire blade by using a ceramic core. The features and size of the ceramic core are reflected in the trailing edge. However, core design considerations must be weighed against trailing edge design considerations. For example, larger core features that create impingement channels in the trailing edge are better for core strength, but larger impingement channels mean reduced flow metering. Hence, a well designed core that balances core considerations with trailing edge cooling requirements is a key aspect of a well designed trailing edge design.
Impingement cooling along the mean camber line in a turbine airfoil trailing edge is known. In this arrangement orifices are cast as part of the trailing edge and are oriented with the mean camber line create high-speed impingement jets of cooling fluid. These impingement jets may impinge a surface between adjacent downstream impingement orifices, and this results in an increased heat transfer rate. Single, double, or triple impingement may occur before the spent cooling fluid is exhausted from the trailing edge into the combustion gas path. The series of impingement orifices also act to meter the flow and this provides a more efficient use of the cooling fluid.
By virtue of their location on the mean camber line the impingement orifices are located between the concave interior surface on the suction side and the convex interior surface on the pressure side of the airfoil. Prior cooling schemes have improved heat transfer by angling the impingement orifices such that they produce impingement jets that impinge the concave and convex interior surfaces. This, in turn, cools the respective exterior surfaces of the trailing edge. Other prior cooling schemes place various surface features on the interior surfaces coincident with the impingement jets. However, operating temperatures of gas turbine engines continue to increase. This leaves room in the art for improvements to cooling of the trailing edge.